1. Field of the Invention
The present invention relates to a vertical film formation apparatus of the batch type for forming a thin film, such as a silicon nitride film (SiN film) on target objects, such as semiconductor wafers, and a method for using the same, and particularly relates to a semiconductor process technique for inhibiting metal contamination inside the process container. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target object, such as a semiconductor wafer or a glass substrate used for an FPD (Flat Panel Display), e.g., an LCD (Liquid Crystal Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target object.
2. Description of the Related Art
In the manufacturing sequence of semiconductor devices, there is used a film formation process for forming a thin film, such as a silicon nitride film, on a semiconductor wafer, such as a silicon wafer. In such film formation processes, a vertical heat processing apparatus of the batch type is often used to perform film formation by chemical vapor deposition (CVD) on a plurality of semiconductor wafers together at a time.
In recent years, owing to the demands for increased miniaturization and integration of semiconductor devices, it has been required to form a thin film of higher quality, such as a silicon nitride film. As a technique for fulfilling the demands to form a thin film of higher quality, there has been proposed a technique for forming an SiN film by ALD (atomic layer deposition) that alternately supplies an Si source gas and a nitriding gas to repeat lamination of films of an atomic layer level or molecular layer level. For example, dichlorosilane (DCS: SiH2Cl2), which has a high adsorbent property, is used as the Si source, and ammonia (NH3) is used as the nitriding gas while being tuned into plasma.
In vertical heat processing apparatuses of the batch type, the process container, wafer boat, and so forth are made of quartz. After a film formation process is repeated, a cleaning is performed to remove reaction products, and then a coating process is performed to cover the inner surface of the process container, the surface of the wafer boat, and so forth with a coating film made of the same material as the product film (which means the product film formed on wafers by the film formation process). This is conceived to prevent particles and contaminants, such as Na, from scattering from theses members (made of quartz) and contaminating the product film. Conventionally, in film formation apparatuses for forming a product film by plasma ALD, a coating process of this kind is also performed by plasma ALD to simplify the control and increase the yield (International Publication No. WO 2004/044970 (Patent Document 1)).
However, where the technique disclosed in the Patent Document 1 is used, it is difficult to satisfy requirements for the Na contamination caused on the product film, which is formed by the film formation process after the coating process, although the requirements are increasingly stricter. In order to solve this problem, there has been proposed a technique for performing the coating process by thermal CVD that simultaneously supplies DCS gas and NH3 gas without utilizing plasma (International Publication No. WO 2007/111348 (Patent Document 2)).